1. Field of the Invention
This invention relates generally to an apparatus and method for use in orthopedic surgery and, more particularly, to an apparatus and method for plugging holes in an acetabular shell component and the associated instruments used for inserting and removing plugs in the acetabular shell component.
2. Discussion of the Related Art
A natural hip joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural hip joint with a prosthetic hip. When implantation of such a hip joint prosthesis becomes necessary, the head of the natural femur is first resected and a cavity is created within the intramedullary canal of the host femur for accepting the hip prosthesis. The hip prosthesis may be inserted and supported within the host femur by cementing the hip prosthesis within the host femur or by using an impact method where the hip prosthesis is snugly fit within and is supported by the host femur. If the acetabulum also needs repair, all remnants of articular cartilage are generally removed from the acetabulum and an acetabular prosthesis which will accommodate the head or ball of the hip prosthesis is affixed to the acetabulum. The acetabular prosthesis is affixed to the acetabulum by means of cement, screws or other appropriate fixation means.
An impact type acetabular prosthesis which is stabilized by means of fixation screws generally includes an acetabular shell component and a polymeric shell liner. The acetabular shell component includes a smooth inner concave surface, a roughened outer convex surface and a plurality of holes passing therethrough for receipt of the fixation screws. The fixation screws may be installed into all of the holes or only some of the holes depending on the patient's requirements. The polymeric shell liner seats against the smooth inner concave surface and acts as a bearing surface for the head of the hip prosthesis. As the hip prosthesis is loaded, micro-motion may occur between the acetabular shell component and the polymeric shell liner, potentially resulting in wear debris being formed between the shell component and the shell liner. Since some of the holes in the shell component may not receive fixation screws, the wear debris may pass through these open holes and out of the shell component.
To seal or cover the holes, some acetabular prostheses utilize plugs to cover the holes formed in the acetabular shell component. For example, U.S. Pat. No. 5,310,408 provides for a closure member which may be pressed into selected openings after implantation of the shell component or removed before implantation of the shell component. U.S. Pat. No. 4,955,325 provides for cement spacers which lock into apertures in the shell to provide for a cement mantel. U.S. Pat. No. 4,955,325 also provides for a threaded plug which is utilized for closing a complimentary threaded center hole in the shell component. However, use of the above-identified plug mechanisms suffer from many disadvantages.
Specifically, in U.S. Pat. No. 5,310,408, the closure members, if inserted into the shell component during manufacture, must be removed before the shell component is implanted, should it be desirable to use the selected holes (i.e. remove by applying pressure on the outer concave side). This procedure reduces the surgical flexibility by requiring a surgeon to determine which closure members should be removed prior to actually implanting the shell component. Moreover, no mechanism for removal of the closure members is taught. Still further, should it be required for the surgeon to plug the various holes with the closure members once the shell component has been implanted into the patient, this increases the surgical time and cost.
In U.S. Pat. No. 4,955,325, the complimentary threaded plug is inserted from the outer convex side of the shell component prior to implantation of the shell component, thereby also reducing surgical flexibility. The use of the complimentary threaded plug may also not provide an effective seal, via the complimentary threads. The cement spacers are also merely used to provide for a uniform cement mantel and do not seal the holes in the shell component because of a bore passing through the cement spacers. Finally, removal of the closure members by an instrument in either of the above-identified devices may create scratches or scars on the inner concave surface of the shell component that will generally require a new shell component to be implanted.
What is needed then is an apparatus and method for plugging holes in an acetabular shell component which does not suffer from the above-mentioned disadvantages. This in turn, will provide more surgical flexibility during implantation of the acetabular prosthesis; reduce the potential for wear debris exiting the acetabular shell component; provide pre-installed plugs that may be removed once the acetabular shell component has been implanted; provide instrumentation to remove the plugs after implantation without the possibility of scratching the inner concave surface of the acetabular shell component; provide a more fluid tight seal; and reduce surgical time, cost and complexity. It is, therefore, an object of the present invention to provide such an apparatus and method for plugging holes in an acetabular shell component.